Extract `Tagged a b`?

[joneshf]

Tagged a b lives in here, but it's really useful a thing—like Const a b useful. Would you be up for pulling it out and depending on it externally?

Also, there are a ton of useful instances missing from it. Whether it stays here or not, would you be up for a PR adding those instances?

[garyb]

Sounds good to me!

[paf31]

Would it go into a new contrib library then? Sounds fine to me.